fix(button,iconbutton): use form-associated mixin behavior

button/internal/button.ts

@@ -16,24 +16,19 @@ import {
   dispatchActivationClick,
   isActivationClick,
 } from '../../internal/events/form-label-activation.js';
-import {
-  internals,
-  mixinElementInternals,
-} from '../../labs/behaviors/element-internals.js';
+import {mixinElementInternals} from '../../labs/behaviors/element-internals.js';
+import {mixinFormAssociated} from '../../labs/behaviors/form-associated.js';
 import {mixinFormSubmitter} from '../../labs/behaviors/form-submitter.js';
 
 // Separate variable needed for closure.
 const buttonBaseClass = mixinDelegatesAria(
-  mixinFormSubmitter(mixinElementInternals(LitElement)),
+  mixinFormSubmitter(mixinFormAssociated(mixinElementInternals(LitElement))),
 );
 
 /**
  * A button component.
  */
 export abstract class Button extends buttonBaseClass {
-  /** @nocollapse */
-  static readonly formAssociated = true;
-
   /** @nocollapse */
   static override shadowRootOptions: ShadowRootInit = {
     mode: 'open',
@@ -43,7 +38,7 @@ export abstract class Button extends buttonBaseClass {
   /**
    * Whether or not the button is disabled.
    */
-  @property({type: Boolean, reflect: true}) disabled = false;
+  declare disabled: boolean; // for jsdoc until lit-analyzer is updated
 
   /**
    * Whether or not the button is "soft-disabled" (disabled but still
@@ -89,13 +84,6 @@ export abstract class Button extends buttonBaseClass {
   @property({type: Boolean, attribute: 'has-icon', reflect: true}) hasIcon =
     false;
 
-  /**
-   * The associated form element with which this element's value will submit.
-   */
-  get form() {
-    return this[internals].form;
-  }
-
   @query('.button') private readonly buttonElement!: HTMLElement | null;
 
   @queryAssignedElements({slot: 'icon', flatten: true})

iconbutton/internal/icon-button.ts

@@ -19,17 +19,15 @@ import {
   afterDispatch,
   setupDispatchHooks,
 } from '../../internal/events/dispatch-hooks.js';
-import {
-  internals,
-  mixinElementInternals,
-} from '../../labs/behaviors/element-internals.js';
+import {mixinElementInternals} from '../../labs/behaviors/element-internals.js';
+import {mixinFormAssociated} from '../../labs/behaviors/form-associated.js';
 import {mixinFormSubmitter} from '../../labs/behaviors/form-submitter.js';
 
 type LinkTarget = '_blank' | '_parent' | '_self' | '_top';
 
 // Separate variable needed for closure.
 const iconButtonBaseClass = mixinDelegatesAria(
-  mixinFormSubmitter(mixinElementInternals(LitElement)),
+  mixinFormSubmitter(mixinFormAssociated(mixinElementInternals(LitElement))),
 );
 
 /**
@@ -40,9 +38,6 @@ const iconButtonBaseClass = mixinDelegatesAria(
  * @fires change {Event} Dispatched when a toggle button toggles --bubbles
  */
 export class IconButton extends iconButtonBaseClass {
-  /** @nocollapse */
-  static readonly formAssociated = true;
-
   /** @nocollapse */
   static override shadowRootOptions: ShadowRootInit = {
     mode: 'open',
@@ -52,7 +47,7 @@ export class IconButton extends iconButtonBaseClass {
   /**
    * Disables the icon button and makes it non-interactive.
    */
-  @property({type: Boolean, reflect: true}) disabled = false;
+  declare disabled: boolean; // for jsdoc until lit-analyzer is updated
 
   /**
    * "Soft-disables" the icon button (disabled but still focusable).
@@ -105,20 +100,6 @@ export class IconButton extends iconButtonBaseClass {
    */
   @property({type: Boolean, reflect: true}) selected = false;
 
-  /**
-   * The associated form element with which this element's value will submit.
-   */
-  get form() {
-    return this[internals].form;
-  }
-
-  /**
-   * The labels this element is associated with.
-   */
-  get labels() {
-    return this[internals].labels;
-  }
-
   @state() private flipIcon = isRtl(this, this.flipIconInRtl);
 
   constructor() {

labs/behaviors/form-associated.ts

@@ -46,15 +46,16 @@ export interface FormAssociated {
   disabled: boolean;
 
   /**
-   * Gets the current form value of a component.
+   * Gets the current form value of a component. Defaults to the component's
+   * `value` attribute.
    *
    * @return The current form value.
    */
   [getFormValue](): FormValue | null;
 
   /**
    * Gets the current form state of a component. Defaults to the component's
-   * `[formValue]`.
+   * `[getFormValue]()` result.
    *
    * Use this when the state of an element is different from its value, such as
    * checkboxes (internal boolean state and a user string value).
@@ -72,25 +73,26 @@ export interface FormAssociated {
   formDisabledCallback(disabled: boolean): void;
 
   /**
-   * A callback for when the form requests to reset its value. Typically, the
-   * default value that is reset is represented in the attribute of an element.
+   * An optional callback for when the form requests to reset its value.
+   * Typically, the default value that is reset is represented in the attribute
+   * of an element.
    *
    * This means the attribute used for the value should not update as the value
    * changes. For example, a checkbox should not change its default `checked`
    * attribute when selected. Ensure form values do not reflect.
    */
-  formResetCallback(): void;
+  formResetCallback?(): void;
 
   /**
-   * A callback for when the form restores the state of a component. For
-   * example, when a page is reloaded or forms are autofilled.
+   * An optional callback for when the form restores the state of a component.
+   * For example, when a page is reloaded or forms are autofilled.
    *
    * @param state The state to restore, or null to reset the form control's
    *     value.
    * @param reason The reason state was restored, either `'restore'` or
    *   `'autocomplete'`.
    */
-  formStateRestoreCallback(
+  formStateRestoreCallback?(
     state: FormRestoreState | null,
     reason: FormRestoreReason,
   ): void;
@@ -238,7 +240,9 @@ export function mixinFormAssociated<
       return this.hasAttribute('disabled');
     }
     set disabled(disabled: boolean) {
-      this.toggleAttribute('disabled', disabled);
+      // Coerce `disabled` in `Boolean()` to ensure that setting to `null` or
+      // `undefined` sets the attribute to `false`.
+      this.toggleAttribute('disabled', Boolean(disabled));
       // We don't need to call `requestUpdate()` since it's called synchronously
       // in `attributeChangedCallback()`.
     }
@@ -282,9 +286,7 @@ export function mixinFormAssociated<
     }
 
     [getFormValue](): FormValue | null {
-      // Closure does not allow abstract symbol members, so a default
-      // implementation is needed.
-      throw new Error('Implement [getFormValue]');
+      return this.getAttribute('value');
     }
 
     [getFormState](): FormValue | null {
@@ -294,13 +296,6 @@ export function mixinFormAssociated<
     formDisabledCallback(disabled: boolean) {
       this.disabled = disabled;
     }
-
-    abstract formResetCallback(): void;
-
-    abstract formStateRestoreCallback(
-      state: FormRestoreState | null,
-      reason: FormRestoreReason,
-    ): void;
   }
 
   return FormAssociatedElement;

labs/behaviors/form-associated_test.ts

@@ -217,27 +217,20 @@ describe('mixinFormAssociated()', () => {
   });
 
   describe('[getFormValue]()', () => {
-    it('should throw an error if not implemented', () => {
-      expect(() => {
-        @customElement('test-bad-form-associated')
-        class TestBadFormAssociated extends mixinFormAssociated(
-          mixinElementInternals(LitElement),
-        ) {
-          override requestUpdate(
-            ...args: Parameters<LitElement['requestUpdate']>
-          ) {
-            // Suppress errors that will occur async when the element is
-            // initialized. This is harder to test in jasmine, so we explicitly
-            // call the getFormValue function to test the error.
-            try {
-              super.requestUpdate(...args);
-            } catch {}
-          }
-        }
-
-        const element = new TestBadFormAssociated();
-        element[getFormValue]();
-      }).toThrowError(/getFormValue/);
+    it('should return the value attribute by default', () => {
+      @customElement('test-default-value-form-associated')
+      class TestDefaultValueFormAssociated extends mixinFormAssociated(
+        mixinElementInternals(LitElement),
+      ) {}
+
+      const element = new TestDefaultValueFormAssociated();
+      expect(element[getFormValue]())
+        .withContext('[getFormValue]() return with no value attribute')
+        .toBeNull();
+      element.setAttribute('value', 'value');
+      expect(element[getFormValue]())
+        .withContext('[getFormValue]() return with value attribute')
+        .toBe('value');
     });
 
     it('should not add form data without a name', () => {